System suitable for controlling etching without the aid of an etchant resistant

ABSTRACT

AN ETCHING SYSTEM HAVING SETS OF PREARRANGED NOZZLES FOR DISPENSING ETCHANT ONTO PREFORMED MASKS IN A PREDETERMINED PATTERN TO ALLOW AN OPERATOR TO CONTROLLABLY ENLARGE THE APERTURES IN A PREFORMED MASK WITHOUT THE AID OF AN ETCHANT RESIST.

Jan. 29, 1974 J. J. FRANTZEN ET AL 3,788,912 SYSTEM SUITABLE FORCONTROLLING ETCHING WITHOUT THE AID OF AN ETCHANT RESISTANT OriginalFiled July 14, 1969 5 Sheets-Sheet 1 Jan. 29, 1974 J. J. FRANTZEN ET AL3,783,912 SYSTEM SUITABLE FOR CONTROLLING ETCHING WITHOUT THE AID OF ANETCHANT RESISTANT Original Filed July 14, 1969 5 Sheets-Sheet 2 ZOrQFm10km Jan. 29, 1974 J, J. FRANTZEN ET AL 3,788,912

SYSTEM SUITABLE FOR CONTROLLING ETCHING' WITHOUT THE AID OF AN ETCHANTRESISTANT Original Filed July 14, 196E: 5Sheets-Sheet :5

DRYING OVEN Z O $2 2 E5 RINSE STATION BLACKENING STATION J. J. FRANTZENSYSTEM SUITABLE FOR CONTRO Jan. 29, 1974 ET AL 3,788,912

LLING ETCHING WITHOUT THE AID OF AN ETCHANT RESISTANT Original FiledJuly 14, 1969 5 Sheets-Sheet 4 Jan. 29, 1974 J. .1. FRANTZEN ET AL3,788,912

SYSTEM SUITABLE FOR CONTROLLING ETCHING WITHOUT THE AID OF AN ETCHANTRESISTANT Original Filed July 14, 1969 5 Sheets-Sheet 5 United StatesPatent Ofice 3,788,912 Patented Jan. 29, 1974 Int. Cl. C23f N02 US. Cl.156-6 Claims ABSTRACT OF THE DISCLOSURE An etching system having sets ofprearranged nozzles for dispensing etchant onto preformed masks in apredetermined pattern to allow an operator to controllably enlarge theapertures in a preformed mask without the aid of an etchant resist.

This is a division of application Ser. No. 841,317, filed July 14, 1969.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates generally to etching systems and, more particularly, to etchingsystems than can controllably etch without the aid of an etchantresistant.

Description of the prior art In a typical colored television picturetube, the shadow mask or aperture mask is located between the electronguns at the rear of the tube and the phosphor coated face plate at thefront, or, viewing face of the tube. Electron beams pass through theopenings or apertures in the shadow mask and impinge upon a suitablecolor producing phosphorus dot on the face plate. Behind each of theseopenings in the shadow mask are three phosphorus dots, a triad, one dotfor each of the primary colors. Typically, around each of these dots isan annular black area which separates the various colored phosphorusdots. During the assembly of the picture tube, the shadow mask is usedas a mask or master pattern for first forming the smaller phosphorus dotpattern and then the larger black surround pattern in the face plate ofthe television tube. This is usually done using photographic techniqueswhich are well known in the industry today. In order to print thesephosphorus dots using known photographic techniques, it is necessary tohave a first set of apertures of predetermined diameter and then toenlarge the diameter of the apertures to a second predetermineddiameter. By utilizing the same mask for both sets of apertures iteliminates problems that could be produced due to different patterns ondifferent masks such as misalignment of the electron beams with thecolor producing phosphorus dots.

The present invention offers as an improved system and method forproducing a mask that can he used to form the first set of apertureesand then reworked to form the second larger set of apertures. Becausethe size of the apertures must be controlled to close tolerances(generally .0002" or less), in order to use the mask as a master patternfor forming, the two patterns on the face plate of the television tube,the etching system must be able to enlarge the apertures in a controlledmanner so that the final diameter of the apertures is the proper size.Numerous methods and systems have been used to controllably enlarge theapertures within the shadow mask. One method involved placing aphotoresist material over the existing aperture pattern to prevent theetchant from etching the apertures beyond a predetermined diameter. In

another method the apertures are initially etched to the largestdiameter with the aid of an etchant resist, then the apertures arereduced in diameter by plating additional material on the mask. Afterthe pattern has been formed with the plated mask the plating material isthen etched away leaving the original mask. These prior art methods arerather time consuming and difiicult to utilize in the mass production ofTV aperture shadow masks.

The present invention eliminates some of the problems associated withthe prior art methods by controllably enlarging the apertures withoutthe aid of an etchant resist. The problems inherent in etching withoutan etchant resist have been overcome by subjecting the mask to a sprayof etchant from a plurality of nozzles for a predetermined time. Themask is also subjected to a cleaning process and rinse process undercontrolled conditions prior to spray etching to ensure that the etchantwill properly etch the mask.

SUMMARY OF THE INVENTION Briefly, the present invention comprises asystem and apparatus having a plurality of spray stations having a setof prearranged adjustable spray nozzles for controllably sprayingetchant on the mask and a means for intermittently moving the pluralityof preformed masks into the plurality of stations. As the mask passesthrough the various stations, the mask is subject to a cleansing action,an etching action, a rinsing action, a desmutting action and a dryingprocess before the enlarged aperture mask emerges from the end of thesystem.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 which is comprised of FIGS. 1a,1b, 1c and 1a, shows a front elevation view of apparatus for cleaning,rinsing, etching, blackening and drying a plurality of preformed masksalong a conveyer like member.

FIG. 2 is a partial front view of an alternate embodiment of a mechanismfor pulling the masks through the various stations.

FIG. 3 is an enlarged view of the suction mechanism for preventingetchant from dripping onto the mask after the etchant supply is shutoff.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1a, referencenumber 15 generally designates the first station in system 10. Station15 is a loading station where masks are placed onto a pair of parallel,endless, spaced chains 11 which transport masks 9 with the preformedshape upward to the various stations. Typically, the masks are loaded byan operator. However, they could also be automatically placed on chains11. Chains 11 are intermittently driven so that the operation or workcan be preformed to the mask while the mask is stationary. After thework operation is completed the chain advances the mask to the nextstation. Although a pair of chains are shown for supporting andintermittently moving the masks through the various stations, othertypes of mask support mechanisms could also be used. For example, a pairof tracks or rails could be provided which would slidably support themasks. FIG. 2 shows such an alternate embodiment for moving along a pairof tracks by a suitable expendable intermittent drive member. Thisalternate embodiment is more fully described in the later portion of thespecification.

Next to loading station 15 is a desitometer station 16 where thediameter of the apertures in the preformed mask can be checked bysuitable means such as a light source and a photocell that measures thelight transmitted through the apertures in the shadow mask. As thenumber of apertures per square inch of surface area is known, the amountof light transmitted through the apertures provides the operator withthe dimensions of the apertures of the shadow mask.

After the masks leave densitometer station 16, the mask enters astripping station 17. Stripping station 17 sprays a cleaning solution onthe surface of the mask to remove any black oxides or other material onthe mask which would have an adverse effect on the etching process. Atypical stripping solution that could be used is hydrochloric acid whichis marketed under the trade name Fremont 348. Typically, strippingstation 17 comprises three sets of spray units. At each of the units themask is subjected to a spray of cleaning solution from nozzles locatedabove and below the mask.

Located adjacent to station 17 is a rinse station 18 that sprays wateron the mask and the chain from a first set of nozzles located above themask and a second set of nozzles located below the mask and the chain.Rinse station 18 washes off any cleaning solution that adheres to themask or chain to prevent the contamination of other stations by thestripping solution.

After the mask has been rinsed to wash off the stripping solution, themask enters an etch station 19 comprised of four separate etching units19a, 19b, 19c and 19d. Each of these units spray etchant for apredetermined time on the mask from a plurality of nozzles located abovethe mask. These nozzles are prearranged as to spacing and height abovethe face of the mask so as to direct a controlled spray of etchant ontothe face of the mask to en large the apertures in the mask to thedesired opening. Typically, ferric chloride is used as an etchant toenlarge the apertures if the mask is formed from cold rolled steel. Bycontrolling the spray of etchant on the mask with the sets of variousnozzles, the apertures can be controllably enlarged without the aid ofan etchant resist. Next to etch station 19 is a second rinse station 20that washes off any excess etchant which is clinging or adhering to themask or the chains.

Located after the rinse station 20 is a second densitometer checkstation 21. The purpose of station 21 is to measure the diameter of theapertures to determine if the apertures of the masks have been enlargedto the proper diameter. If the diameter of the aperture of the mask isproper, the mask moves into a desmut station 22 that removes the carbonparticles on the surface of the mask. The typical mask formed from coldrolled steel contains carbon particles. As these carbon particles arenot affected by the etchant that is used to etch away the steel mask,they must be removed by spraying a carbon cleaning solution on the mask.A typical cleaning or desmut solution suitable for removing these carbonparticles is phosphoric acid.

The next station is a third rinse station 23 that washes off anydesmutting solution on the mask. From rinse station 23 the mask enters ablackening station 24 that contains five separate blacking units thatspray a blacking agent on the mask from above and below the mask. Theblacking agent produces a coating on the outside of the mask thatprotects the mask from oxidation during its latter handling and usagesteps. Typically, a suitable blacking agent such as iron phosphate issprayed on the mask to protect its surface. However, other protectiveagents could also be used.

After blackening station 24 there is a fourth rinse station 25 thatwashes off excess blackening agent on the mask. Located after rinsestation 25 is a deionized water rinse station 26 that sprays deionizedwater on the mask to remove any contaminants on the mask. The deionizedwater also assists in setting the blackening agent on the mask.

The last station in the system is a drying station 27 that forces warmair over the mask to evaporate any moisture on the surface of the mask.

The foregoing has been a brief diseription of the various functions ofthe stations within the system. A more detailed description of theoperation of the apparatus and the various stations will not be given.

To initiate the action an operator loads preformed masks 9 onto theconveyor at the first loading station. As the masks are identical, theyare all identified by reference number 9. Typically, the conveyingstation 30 comprises a pair of endless tracks which are derived by asuitable drive unit such as an electric motor 31. The chain drive isintermittently movable, that is, the chain advances for a predeterminedtime and then remains stationary for a predetermined time and thenadvances again for a predetermined time. During the time interval thechain and masks are stationary, the stations are in an operativecondition and correspondingly during the time interval the chain andmasks are moving the stations are in an inoperative condition. This typeof operation allows the mask to move from station to station or fromunit to unit within a particular station without having the operation ofone unit or station having an adverse effect on and adjacent stationthrough splattering of the various solutions out of the variousstations. The first movement of the chain 11 moves mask 9 intodensitometer check station 16 to measure the diameter of the apertures.

After the diameter of the apertures are measured in densitometer checkstation 16, a pressure signal is sent to pressure actuated cylinder 42to raise slidable door located at the entrance to stripping station 17.Similarly, pressure signals are sent to all the pressure actuatedcylinders to raise all the slidable doors at the front and rear of thestations.

As all the slidable doors and their operation are identical, they willnot be described in detail. The main purposes of the slidable doors isto seal the chamber within the stations to provide a closed returnsystem and also to prevent etchant and other chemicals which are used inthe various station from splashing out of the station to contaminate theadjacent station or the mask in the adjacent station.

' After door 40 is raised, mask 9 advances into stripping station 17where the mask remains for three intervals of time. For illustrativepurposes assume that the time interval chain 11 is at lest is 15seconds. Thus, mask 9 is in station 17 for a total work time of 45seconds. During this time the mask is first subjected by spray fromabove by a first set of nozzles 50 and from below by a second set ofnozzles 50a. After the mask has been subjected to spray from nozzles 50and 50a, chain 11 advances mask 9 into the second work position betweenroller chain supports 51 where mask 9 is subjected to spray from aboveby a third set of nozzles 52 and from below by a fourth set of nozzles52a. After being subjected to spray from nozzles 52 and 52a, chain 11advances mask 9 into the third work position within station 17. In thethird work position mask 9 is subjected to spray from above by a fifthset of nozzles 54 and from below by a sixth set of nozzles 54a. Thevarious work positions within station 17 are not individually separatedfrom one another as the splatter or spray of cleaning solution from theadjacent nozzles is not harmful and as the cleaning solution onlyremoves surface coatings on the mask and does not attack and erode themask. An example of a typical stripping solution is Fremont 348 which isa diluted hydrochloric acid. When this solution is sprayed onto thesurface of the mask through the various sets of nozzles it removes anyoxides on the mask which would act as an etchant resist and produceuneven etching during the multiple step etching process.

After mask 9 leaves stripping station 17, it enters into rinse station18 through the aforementioned slidable doors. In station 18 masks 9 andchains 11 are subjected to a water spray rinse from nozzles 55 locatedabove the mask and from nozzles 55a located below the mask. As cleanwater is continually being supplied to nozzles 55 and nozzles 55a andthe rinse water is disposed of, it leaves the mask in a condition wherethe only foreign solution on the mask is the water. This preventscontamination of the etching station 19 due to any material or solutionfrom stripping station 17 which could adhere to the mask and follow themask into the etching station 19 where it would become part of therecirculating etchant.

After mask 9 has "been subjected to a spray rinse for a predeterminedtime interval, the doors on the sides of rinse station 18 automaticallyopen. After the doors are opened, chain 11 advances moving mask 9 intoetching station 19. Etching station 19 comprises four separate etchingunits 19a, 19b, 19c, and 19d which successively sprays an etchantsolution, such as ferric chloride, onto the top of a particular mask.First, a set of prearranged nozzles 60 spray etchant onto the mask for apredetermined time. Nozzles 60 are spaced vertically and horizontally ina preformed pattern to enable the etchant to be properly distributedover the top surface of the mask. Each of the nozzles are adjustablevertically so that the spacing of the nozzles above the mask can becontrolled to thereby vary the spray pattern of the etchant on the mask.Each nozzle has a flow meter 61 and a regulating valve 62 so that theamount of etchant supplied through each nozzle can be preselected by theoperator. Each of the nozzles is connected to a plenum chamber whichprevents back pressure at any one nozzle from affecting the flow ofetchant through the other nozzles. The purpose of the flow meter is toprovide a convenient visual indication as to whether or not the etchantis flowing through the nozzle. If one of the nozzles should becomeclogged and thus reduce the supply of etchant to a localized area of themask, it would produce an improperly etched mask. Therefore, it isnecessary to have a convenient method'of determining whether the nozzlesare properly dispensing the etchant onto the mask.

After mask 9 has been subjected to etchant spray from set of nozzles 60for a predetermined time, the supply of etchant is shut off to preventany etchant from dripping from the nozzles onto the mask. If etchantshould drip onto the mask, it would produce enlarged openings inportions of the mask and it could also bend the thin mask by the forceof the etchant droplets landing on the mask. In order to ensure that anyetchant in the supply line does not drip from nozzles 60 and onto themask 9, there is provided a suction system which is shown in FIG. 3.

In order to control the enlargement of the apertures in the domed mask,it is preferred to space the adjustable nozzles 60 in a vertical patternthat somewhat follows the general dome-shaped appearance of mask 9.However, it should be understood that the vertical spacing of thenozzles above mask 9 can be varied to control the spray pattern on mask9. In addition, more or less etch-ant can be sprayed through theindividual nozzles by adjusting the individual valves 62 connectedtogether. In a typical operating unit approximately 30 nozzles arelocated above the mask in a spaced relationship to produce an etchantspray pattern that can enlarge the apertures in mask 9 in a controlledmanner. However, no limitation is intended thereto.

Located within the etching station 19 is a second etching unit 19b whichhas a second set of prearranged nozzles 70. Nozzles 70 are preferablyarranged in a different pattern and spacing than nozzles 60 so as toproduce a different etchant spray pattern on mask 9. Similarly, a thirdset of prearranged nozzles 75 are located in etching unit 190. Nozzles75 are also preferably arranged in different pattern and spacing thannozzles 60 or '70 to produce a different etchant spray pattern on mask9.

A final etching unit 19d contains still another set of prearrangednozzles 76 which are preferably located in a different pattern andspacing than the previous nozzles so as to produce a different spraypattern on mask 9. By

6 having four sets of nozzles located in different patterns andindividually adjustable as to vertical spacing and etchant flow, anoperator can select the proper adjustments through a trial and errorprocedure so that he can controllably enlarge the apertures in mask 9without an etchant resist. Etching station 19 has all of the differentses of nozzles located above the mask so that the etching is performedprimarily on the convex side of dome-shaped mask 9. In the etchingenlarging process it is usually necessary to uniformly enlarge theapertures throughout the mask. To accomplish a uniform enlargement ofthe apertures, it is necessary to space the nozzles at various heightsand at various locations but the preferred location is one in which theend points of the nozzles generally conform to a three dimensionalpattern that is similar to the dome-shape of the mask. However, thethree dimensional pattern that the end points of the nozzles definegenerally is more pronounced than the dome-shape of the mask. However,no limitation is intended thereto, as one of the features of the presentsystem is its aspect of etchant supply control through flow adjustment,prearranged spacing of nozzles, with respect to one other, variablespacing of the nozzles above the mask and the different sets of nozzlesto produce the desired etchant spray pattern. Although the etchant spraynozzles are shown located above the masks, it is envisioned that withsuitable adjustment of the nozzles and the equipment, the nozzles couldbe located horizontally rather than vertically as shown in the system.

Located after etch station 19 is a rinse station 20 that sprays water onmask 9 to rinse off any etchant on the surface of the mask. If theetchant were not rinsed off it would continue to erode the aperture maskand thus produce localized etching that would produce oversizedapertures in certain areas and consequently a mask that is unacceptablefor use in a television tube. After mask 9 passes through the rinsestation 20, the mask enters a densitometer check station 21 where theaperture size is checked to determine if the unit has been properlyetched.

After the mask leaves densitometer station 21 it enters into a desmutstation 22 which sprays a desmutting solution on the mask from nozzles22a located above the mask and nozzles 22b located below the mask.Typically, this desmutting solution could be phosphoric acid or the likewhich removes the carbon particles on the surface of the mask. As themask is usually made from cold rolled steel containing carbon particlesand is usually etched with ferric chloride, which etches the metal butnot the carbon particles, it is necessary to remove these carbonparticles from the mask by a second etchant. After removal of the carbonparticles in desmut station 22, the mask enters into a rinse station 23that rinses off any excess phosphoric acid or desmutting solution onmask 9. The mask then enters a blackening tank 24 where the mask issprayed from above and below with an iron phosphate solution. Theblackening station contains five sets of nozzles 80, 81, 82, 83 and 84which are located above the mask and five sets of nozzles 85, 86, 87, 88and 89 which are located below the mask. These nozzles spray blackeningsolution completely over the top and bottom of the mask to produce acoating that will give corrosion resistance and this prevent oxidationof the mask before it is put into use. In order to insure properprotection of the mask, the mask is subjected to spray from these fivesets of nozzles for a time interval of five times the present which, inthis case, would be 75 seconds.

After the mask leaves blacking station 24, it enters into rinse station25 that sprays top water onto the mask from nozzle 25a and 25b. Thesenozzles remove any excess blacking agent on the mask The mask thenenters a final rinse station 26 where deionized water is sprayed on themask to remove any contaminants on the mask. The deionized water sprayalso assists in settling the blacking agent on the mask.

The last station in the system is a drying oven 27 that force warm airto evaporate any water that is on the mask.

Referring to FIG. 2, there is shown an alternate embodirnent of theintermittent drive mechanism for advancing the mask through the variousstations. Typically, the intermittent drive mechanism comprises a set ofmask support racks 101 having a hook 102 located at the front of thesupport racks. During travel through the various stations hook 102 formsinterlocking engagement with rear bar 115 of the mask support racklocated in front thereof. This produces an interconnected set of masksupport racks that can be pulled through the various stations on a racksupport track by a rotatable extendible advance mechanism 105. Advancemechanism 105 comprises a pair of arms that are rotatably mounted tosupport 107 through a shaft 108. Located on the lower end of member 106are a pair of telescoping rods 110 that are extendible into engagementwith the backside of hook 102 through a pressure actuated mechanism 112having a linear ex tendible rod 113.

FIG. 2 shows advance mechanism 105 in the position prior to advancingthe train of masks. To advance the masks a signal is sent which rotatesshaft 108 and advance mechanism counterclockwise until the mask supportrack has moved up one rack length. As the mask support rack movesforward, the mask support rack immediately ahead of the advancemechanism drops onto a set of rollers 116 that support and drive therack into the drying station. Rollers 116 are at a slightly lowerelevation than track 117 so that the forward mask support rackdisengages from the rear mask support rack as the mask drops ontorollers 116.

After advance mechanism 105 has advanced the mask support rack forward,a pressure signal is applied to pressure cylinder 112 which causes rod113 to retract thereby retracting telescoping pusher rods 110 into arm106. This allows one to rotate the'advance mechanism clockwise into theposition shown in FIG. 2 where a pressure signal is applied to thepressure cylinder 112 to extend the pusher arms 110 into frictionalpushing engagement with the back or another mask support rack. This typeof arrangement provides an intermittent drive unit for advancing onemask at a time through the various stations of the system. This systemolfers an advantage over the chain type of supports in that there is nota continual wear motion of a chain as it passes through the variouswashing, etching and heating stations which could cause deterioration ofthe chain.

Referring to FIG. 3, reference numeral 150 designates the suction systemfor preventing etchant from dripping onto the mask. Although suctionsystem 150 is shown connected to etching unit 19a, the other etchingunits similarly have a suction system to prevent dripping of the etchantonto the mask.

During the spray etching process a pump 151 draws etchant from receiver152 through pipe 153 and discharges it under pressure through outlet154. The etchant flows through an open pneumatic valve and into pipe 158and pipe 159. The etchant in pipe 158 flows through a plenum chamber 160and the various flow meter valves, and nozzles to issue in the form of aspray from the end of nozzles 60. The etchant in pipe 159 flows intoreceiver 152 through an orifice 161 or other suitable fluid flowresistance. By closing valve 155 with etchant flowing through both pipe158 and pipe 159, the supply of etchant to both pipe 158 and pipe 159 isshut off. Because of the momentum of the fluid in pipe 159 and thelesser gravitational field, the fluid in pipe 159 continues to flow fromnozzle 161 which produces a slightly lower pressure in pipe 158. Thislower pressure momentarily stops the flow of fluid through nozzles 60because of the back pressure in the nozzles. Typically, the etchantissuing from nozzles 60 abruptly stops for a period of two to fourseconds which is sulficient time to advance the mask from beneathnozzles 60 to a second position beneath.

Another embodiment for preventing the etchant from falling on the maskswhen the etchant supply is shut off involves sliding a tray between themask and the nozzles as soon as the supply of etchant to the nozzles isshut off. The tray then catches any etchant droplets that would fall onthe mask and cause damage to the mask.

We claim:

1. The method of controllably enlarging apertures in a preformed metalmask without an etchant resist comprising the steps of:

cleaning said preformed metal mask to remove materials that would act asan etchant resist;

subjecting said preformed metal mask to etchant issuing in apredetermined spray pattern by employing a plurality of spray changerswherein multiple spray heads are vertically arranged to apply asuperimposed spray pattern on the surface of said preformed metal maskfor a predetermined time to thereby enlarge the apertures in saidpreformed metal mask;

abruptly shutting off the spray pattern of etchant issuing from saidmultiple spray heads by controlling the pressure in said multiple sprayheads to prevent supplying further etchant to said preformed metal maskwhich would continue to etch said preformed metal mask; and

removing any excess etchant that adheres to said preformed metal mask.

2. The method of claim 1 wherein said mask is subjected to etchantissuing in a second predetermined spray pattern for a predetermined timeto further enlarge the apertures in said preformed metal mask.

3. The method of claim 1 including the step of subjecting said preformedmetal mask to etchant issuing in a third predetermined spray pattern fora predetermined time to further enlarge the apertures in said mask.

4. The method of claim 3 including the step of subjecting said preformedmask to etchant issuing in a fourth predetermined spray pattern for apredetermined time to further enlarge the apertures in said preformedmetal mask.

5. The method of claim 4 including the step of decreasing the etchantsupply after the predetermined time has elapsed to prevent etchant fromdripping onto said preformed metal mask.

6. The process of controllably enlarging apertures in a preformed domedmetal mask having a plurality of apertures therein by use of an etchantand without the use of an etchant resist on said preformed domed metalmask comprising the steps of:

(a) cleaning the preformed metal mask having a plurality of aperturestherein to remove materials from said preformed metal mask that wouldact as an etchant resist;

(b) subjecting the preformed metal mask having a plurality of aperturestherein to a predetermined spray pattern by employing a plurality ofspray chambers wherein multiple spray heads are arranged to apply asuperimposed spray pattern on the surface of said preformed metal maskfor a predetermined time to thereby enlarge the apertures in saidpreformed metal mask;

(0) abruptly decreasing the etchant issuing from said multiple sprayheads by controlling the pressure in said multiple spray heads toprevent supplying further etchant to said preformed domed metal maskwhich would continue to enlarge the aperture in said preformed domedmetal mask;

(d) measuring the size of the apertures in the preformed domed metalmask to determine if the apertures have been enlarged to the properdimension.

7. The process of claim 6 including the step of applying the spraypattern of etchant on the domed portion of the preformed aperture mask.

8. The method of claim 7 wherein the preformed domed mask is sprayedwith etchant from at least two different positions and at least twodiiferent intervals.

9. The method of claim 8 wherein the preformed domed mask is sprayedwith etchant from at least three diiferent positions and at least threedifferent intervals.

10. The method of claim 9 wherein the preformed domed mask is sprayedwith ctchant from at least four different positions and at least fourdiiferent intervals.

10 References Cited UNITED STATES PATENTS 2,750,524 6/1956 Braham 313-862,961,314 11/1960 Amdursky et a1. 9638 JACOB H. STEINBERG, PrimaryExaminer U.S. C1. X.R. 156-2, 18

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 788,912 Dated January 29, 1974 Inventor(s) John J. Frantzen and Charles M.Lund It is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

In Claim 1, line 8, "changers" should be chambers Signed and sealed this23rd day of April 197A.

(SEAL) Attest:

EDWARD MQI LLTCEEEIP JR. V G. MARSHALL DANN Attosting OfficerCommissioner of Patents FQRM o-1oso (10-69) USCOMM-DC 60376-P6Q a uos.sovgmmzm PRINTING OFfI CE: was o-ses-sai

